The present invention relates to a photoelectric conversion device having a novel structure and, more particularly, to a photoelectric conversion device employing a flexible substrate having poor thermal resistance. Also, the invention relates to processing of this flexible substrate such as formation of a coating on the substrate and, more particularly, to a method of treating the flexible substrate with a plasma when a solar cell or the like is fabricated by the use of a flexible organic film instead of a solid substrate.
The market has required smaller, thinner, and even lighter electronic and electric parts. Various materials have begun to be used to fabricate these parts.
Photoelectric conversion devices such as solar cells also show such a tendency, and devices of various specifications have been proposed. Among others, thin and light devices using a substrate made of a flexible organic or metal film have attracted attention because of the possibility of application to other electrical appliances and industrial machines.
Of photoelectric conversion devices using these flexible substrates, photoelectric conversion devices employing substrates made of organic materials have attracted attention because of their cost, characteristics, and workability. Photoelectric conversion devices of this type have begun to become the mainstream of photoelectric conversion devices having flexible substrates. Flexible substrates made of organic materials have numerous advantages of having high workability and being light in weight over substrates made of thin metal materials.
The structure of a photoelectric conversion device using a flexible substrate made of such an organic material is diagrammatically shown in FIG. 7, where three photoelectric elements are connected in series on a flexible substrate 1 to form an integrated photoelectric conversion device. Each of the photoelectric elements comprises a first electrode 71, a semiconductor layer 72 consisting of a non-single crystal, and second electrodes 73, 74. In this example, light impinges on the second electrodes. Therefore, one second electrode 73 is made of an ITO that is a transparent electrode material. The other second electrodes 74 are grid-like auxiliary electrodes. The second electrodes 74 are connected with the first electrodes 71 of adjacent photoelectric conversion elements. The elements are connected in series. The output from this photoelectric conversion device is developed between copper leads 75 which are soldered to the second electrodes.
Substrates having poor thermal resistance such as the aforementioned flexible substrates made of organic materials are not sufficiently resistant to heat compared with substrates made of other materials. Polyimide film which is said to be resistant to heat can withstand high temperatures of about 300 to 350xc2x0 C. at best. For this reason, when photoelectric conversion devices are manufactured, application of heat is avoided as fully as possible. This method has been put into practical use.
However, after a photoelectric conversion device is fabricated, output leads must be provided to permit the use of the device. The output leads are connected with the second electrodes normally by soldering. To fuse the solder, it is necessary to apply heat locally.
Consequently, excessive heat is applied to only a part of the organic material of the flexible substrate. As a result, only this part deforms thermally. If the leads are bonded to the electrodes of the photoelectric conversion device at a temperature at which no thermal deformation takes place, then a sufficient bonding strength cannot be obtained. Under this condition, the electrical conduction deteriorates, or the bonded portions peel off, thus impairing the reliability. Hence, it is desired to improve these output leads.
Where a photoelectric conversion device is fabricated from such a flexible material by the prior art techniques, handling of the substrate has posed problems. Especially, where a semiconductor coating or the like is formed by chemical vapor deposition or other similar method, the flexibility of the substrate presents problems. Therefore, when such a substrate is used, the production facility has been required to have a special means for holding the substrate, unlike the case in which other solid substrates are employed.
A so-called roll-to-roll method has been generally accepted as a method of holding the substrate. This method begins with pulling out a flexible substrate from a roll. The substrate is fed into a plasma processing apparatus or plasma processing chamber, where the substrate is processed. Then, the substrate is rewound into a roll.
In the case of a plasma processing machine making use of the conventional roll-to-roll method, a substrate is placed substantially parallel to electric discharge electrodes located in a region where plasma processing is performed. The substrate is slowly and continuously supplied from the roll and passed through the processing region to treat the substrate with a plasma.
One example of this machine is disclosed in Japanese Patent Laid-Open No. 34668/1984. This disclosed machine is designed to form a film. The reaction chamber of this machine and its vicinities are schematically shown in FIG. 9, where a flexible substrate 201 is wound into a roll 220. The substrate is continuously fed into the reaction chamber, 221, from the roll 220. A pair of parallel-plate electrodes 222, 223, a reactive gas supply system 225, and an exhaust system 226 are mounted inside the reaction chamber 221. The continuous flexible substrate 201 passes over or by the cathode of the parallel-plate electrodes substantially parallel to them. In this structure, a film is formed on the substrate. The substrate may also be positioned on the side of the anode and processed. The substrate 201 supplied in this way is treated with a plasma while passing through the processing region close to the electrodes. That is, the substrate is treated with a plasma or a film is formed while the substrate stays in the processing region.
In the known plasma processing machine described above, a set of discharge electrodes can treat only one roll of substrate. Hence, the throughput of the plasma processing is low. In the case of silicon of a non-single crystal used for photoelectric conversion device, a film is grown at a rate within a range from 0.1 to 10 xc3x85/sec to secure the required semiconductor characteristics, i.e., to prevent the film quality from deteriorating. It is usually necessary that a semiconductor film of a photoelectric conversion device have a thickness of about 0.3 to 2 xcexcm. Therefore, the substrate must stay in the processing region for a long time. In consequence, the plasma processing region, or the electrodes, must be made long, or the substrate must be passed through the region at a quite low speed.
Where the electrodes are made long, the dimensions of the reaction chamber are increased. That is, the plasma processing machine occupies a large area. This is a heavy burden on mass production. If the substrate conveyance speed is decreased, the throughput of the plasma processing drops, thus hindering mass production. More specifically, in the case of the above-described semiconductor consisting of a non-single crystal, if a film 1 xcexcm thick should be formed within a reaction chamber about 1 m long at a deposition rate of 1 xc3x85/sec, then the substrate is transported at 0.1 mm/sec. If a roll having a length of 100 m is treated, as long as about 278 hours are required.
Consequently, there is a demand for a machine which relies on the roll-to-roll method and treats substrates at a higher speed or improves the throughput of the machine. Whether electronic devices using flexible substrates can be mass-produced or not depends heavily on this point.
The present invention resides in a photoelectric conversion device which takes the form of a thin film and is formed on a substrate having poor thermal resistance e.g. an organic resin substrate. The device has output terminals to permit the output from the device to be taken out. The output terminals are mounted on an opposite surface of said substrate to the surface of the substrate on which the device is formed. The photoelectric conversion device further includes electrical connector portions (conductors) for electrically connecting the output terminals with the electrodes of the device.
In one feature of the invention, the substrate of the photoelectric conversion device described just above is flexible, and the electrical connector portions are located in holes (openings) formed in the flexible substrate.
In another feature of the invention, the substrate of the photoelectric conversion device described just above is flexible, and the electrical connector portions are located at end surfaces of the flexible substrate, that is, the electrical connector portions are provided on sides of the flexible substrate.
Also, the present invention resides in a photoelectric conversion device which takes the form of a thin film, is formed on a substrate having poor thermal resistance, and has output terminals and electrical connector portions. The output terminals permit the output from the device to be taken out, and are mounted on a surface opposite to the surface of the substrate on which the device is formed. The electrical connector portions electrically connect the electrodes of the device with the output terminals, and are made of the same material as portions of the electrodes of the device.
In any of the novel photoelectric conversion devices described above, output leads are provided to permit the output from the photoelectric conversion device to be taken out. When the device is provided with the output leads, the leads are bonded to the device independent of electrical connection of the leads with the electrodes of the device. Thus, a sufficient bonding strength is accomplished without applying high temperature locally. Therefore, the output terminals are mounted on the surface of the substrate opposite to the photoelectric conversion device. The output terminals are bonded to the substrate. The bonded output terminals are electrically connected with the electrodes of the device by an electrically conductive material. In this way, the output terminals having sufficient bonding strength can be mounted without applying excessive heat to the substrate which has poor heat resistance.
The present invention is also intended to solve the aforementioned problems. It is an object of the invention to provide a method of treating flexible substrates with a plasma with a high productivity. In order to treat the flexible substrate with a plasma, the substrate is continuously supplied into a reaction chamber in such a way that the total length of the substrate existing in a plasma processing region formed by electrodes is longer than the length of these electrodes.
A plasma processing method in accordance with the present invention comprises the steps of:
exposing a substrate to a plasma generated adjacent to an electrode provided in a chamber (or a plasma generated adjacent to an electrode and enclosed within a frame structure provided in a chamber) in order to perform a plasma processing on said substrate; and
conveying said substrate during said plasma processing,
wherein length of said substrate in said plasma is longer than that of said electrode. Said substrate can be moved from a roll to another roll.
One example of method of supplying the flexible substrate in such a way that the total length of the substrate existing in a plasma processing region formed by electrodes is longer than the length of these electrodes is illustrated in FIG. 8, where the flexible substrate, 201, is made to take a zigzag course within the plasma processing region, 204, between a pair of electrodes 202 and 203 by rollers such as 205. In this case, the total length of the flexible substrate 201 existing inside the plasma processing region is increased as the number of turns is increased.
The conventional method utilizing the prior art roll-to-roll scheme as typically shown in FIG. 9 makes use of the dark portion close to the cathode or anode for plasma processing. On the other hand, the present invention makes positive use of a positive column produced by a plasma discharge, thus improving the productivity of the plasma processing. In FIG. 8, the flexible substrate is supplied substantially perpendicular to the surfaces of the discharge electrodes 202 and 203. The direction of supply is not limited to this direction. Similar advantages can be obtained by supplying the substrate parallel or at an angle to the surfaces of the electrodes as long as the total length of the substrate staying in the plasma processing region is longer.
Where a coating is formed by plasma processing, the surface of the substrate is preferably parallel to the direction of gravity. In particular, when a coating is formed, dust and flakes are produced. Therefore, if the surface of the substrate is parallel to the direction of gravity, then the dust and flakes are prevented from depositing onto the substrate. Hence, the surface of the substrate can be made clean. Also in this case, the angular relation between the substrate surface and the electrode surface can be set at will.
The novel method of treating a flexible substrate with a plasma makes use of a positive column more positively in the manner described now. A plasma discharge region is established which has such a frame structure as to confine a plasma discharge within a reaction chamber where plasma processing is performed. The substrate is continuously supplied into the frame structure so that the substrate takes a zigzag course. In consequence, a high productivity can be achieved. Especially, this structure can make the plasma discharge region uniform and hence can realize homogeneous plasma processing.
Since the novel method makes positive use of an electric discharge in a positive column, two rolls of substrate can be supplied in a back-to-back relation into the plasma processing region. In this case, the throughput can be doubled exactly. However, it is necessary to hold the surfaces of the substrates by rollers or the like in order that each substrate take a zigzag route. For this purpose, the surface of each substrate is not totally held but rather partially supported.
The total length of plural substrates existing in the plasma processing region can be made longer than the electrodes by supplying the substrates parallel to the electrodes without taking a zigzag course. In this case, numerous facilities for supplying the substrates are necessary but this method has the advantage that the rolls do not directly touch the substrate surfaces.
Other objects and features of the invention will appear in the course of the description thereof, which follows.